The 2012 end-date is based on the "end-point" or the date of 18.104.22.168.0 in the Maya Long Count Calendar. This is a completely different calendar from the 52-year Calendar Round, and there was a lot of variation across the lands inhabited by the Maya and Aztecs as to when the Calendar Round re-started. John Major Jenkins gives several of the variations in his book ‘Tzolkin’. There is only one known variation that re-starts in 2012, and that is the ‘Tikal’ version, which re-starts not in December 2012, but on April 2nd 2012.
Aztec called the PleiadesTianquiztli, which means the “gathering place,” and was considered an important sign of the continuation of life: on midnight every 52 years it appeared directly overhead and assured the ancient Americans that the world would not come to an end. The Aztecs perform a special religious ceremony called the Dance of the New Fire (or Ceremony of the New Fire) once every 52 years to ensure the movement of the cosmos and the rebirth of the sun. This 52 year time period also corresponds to the 260-day religious calendar (Tonalpohualli in Aztec, or Tolkin in Mayan) when it interlocks with the 365-day civil calendar (Xiupohualli in Aztec or Haab in Mayan). Every 52 Haab solar years (73 Tolkin years) these calendars coincide. This was sometimes called by the Aztecs the Calendar Round. The 52 year cycle was said to begin when the Pleiades crossed the fifth cardinal point or the zenith of heaven at midnight. Sometimes not only is the Pleiades in its zenith over Mesoamerica, but this alignment also comes into a full conjunction with the sun (as we will see again in the 21st Century). In addition, two 52 year cycles (104 years) coordinate with a further alignment with Venus (symbolic of the female creative form on a local scale).